A method of the kind mentioned in the opening paragraph is known from European Patent Application No. 164,281, corresponding to U.S. Pat. No. 4,704,302. In the method described therein, the starting material is a substrate of monocrystalline silicon. Oxygen or nitrogen ions are implanted under a top layer of the substrate. The ions react at this area with the silicon present, as a result of which the latter is converted into silicon oxide and silicon nitride, respectively. Ultimately, the semiconductor body has under the top layer a buried layer of silicon oxide and silicon nitride, respectively.
A disadvantage of the known method described is that, in order to form a good insulating buried layer, in this method the oxygen or nitrogen ions must be implanted at a high dose. In this Patent Application, a dose of 10.sup.18 to 3.times.10.sup.18 ions/cm.sup.2 is mentioned. As a result, the implantation is of long duration and very expensive and a comparatively large number of lattice defects and stresses are produced in the top layer.